In
surface-enhanced Raman scattering, Ag nanoparticles are broadly
employed. However, their lack of oxidation resistance means that their
performance diminishes and is difficult to repeat. In this study,
with addition of xylan, Au–Ag core–shell and alloy nanoparticles
were prepared. Besides functioning as a reducing and stabilizing agent
for Au–Ag bimetal nanoparticles, xylan protected them from
oxidation and aggregation and created hot spots between interconnected
nanoparticles. By seed-mediated methods, Au–Ag hollow alloy
and Au@Ag core–shell nanoparticles with different shell thicknesses
were prepared. More spherical and larger core–shell nanoparticles
were prepared by an optimized dosage of xylan without the generation
of excess Ag nanoparticles. Furthermore, the Au@Ag nanoparticles showed
enhanced stability against oxidation and corrosion by H2O2 with the packing of xylan. The Raman enhancement performance
of xylan-capped Au@Ag nanoparticles with optimized shell thickness
to 4-mercaptobenzoic acid was better than that of Au–Ag alloy,
neat Au and Ag nanoparticles. The Au@Ag nanoparticles could detect
4-mercaptobenzoic acid with a greater sensitivity and its limit of
detection was 1 nM. Moreover, xylan-capped Au@Ag nanoparticles could
detect food contaminant like Sudan I with a limit of detection as
low as 0.126 ppm. Therefore, this work not only offers a new method
for high-value utilization of xylan but also presents a simple, green,
and ultrasensitive surface detection technique for the assessment
of food/environmental safety.
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